Efficiency of Calcium Silicate and Carbonate in Soybean Disease ...

2050 A. Nolla et al.susceptibility of cereals, such as rice (Oryza sativa) and several dicotyledons,to fungal attack (Jones and Handreck, 1967; Menzies and Bélanger, 1996).Many independent studies have confirmed the importance of Si in resistanceto abiotic [iron (Fe), manganese (Mn), and sodium (Na) toxicity] andbiotic (insects and fungi) stresses. Silicon accumulation and deposition in theepidermal cells can be an effective mechanical barrier to fungal penetration.However, the mechanical barrier made by Si in the epidermal cells is not theonly mechanism of prevention of fungal penetration or insect attack. Recentresearch results suggest that Si acts in the host tissue by altering the signals betweenhost and pathogen, resulting in a faster and more extensive activation ofplant defense mechanisms, as shown for cucumber (Cucumis sativas) (Samuelset al., 1991; Chérif et al., 1994; Marschner, 1995).Silicon can form complexes with phenolic compounds and increase theirsynthesis and mobility in the apoplasm (Menzies et al., 1991). A quick depositionof phenolic compounds or lignin in the infection courts is a defensemechanism against a fungal attack, and the presence of soluble Si facilitatesthis resistance mechanism (Menzies et al., 1991).Plant resistance to diseases can be enhanced by the alteration of plantresponses to a pathogen challenge, by increasing toxin synthesis (phytoalexins),which can act as inhibitory and repellent substances, or by promoting theformation of biochemical barriers (Marschner, 1995). Phytoalexins are smallmolecules produced in the plant after a microorganism infection or stress andplay an important role in resistance to diseases and pests. Frequently, phytoalexinsare also toxic to the host, killing the cells as it is accumulated. Resistanceto a pathogen is observed when these compounds accumulate quickly and inhigh concentrations in the infection court, resulting in pathogen death (Fosket,1994). Several flavonoids in legume (e.g. peas, soybean) root exudates canact as suppressors of certain pathogenic fungi, and are considered phytoalexins(Dixon, 1986; Hartwig, 1994). In plant-pathogen interactions, certain finalproducts of flavonoid biosynthesis act as phytoalexins in plant defense reactions(Hahlbrock and Scheel, 1989; Peters and Verma, 1990).Broad-leaf plants, such as soybean and cucumber, are characterized inrelation to Si contents and proportions of Si/Calcium (Ca) as intermediate (1%–3% dry weight), meaning that when the Si concentration in the environmentis high, the plants contain a considerable amount of Si; there is evidence thatthese plants transport Si freely from the root system to their canopies (Miyakeand Takahashi, 1995).Soybean stem canker is a disease caused by a fungus with two developmentalphases: (1) the anamorph, called Phomopsis phaseolif. sp. meridionalis,found in infected tissues, which disseminates through conidia, produced in pycnidia,during the growing season; and (2) the teleomorph, known as Diaporthephaseolorum f. sp. meridionalis (Dpm) (Morgan-Jones, 1989), responsible forthe first infections in the subsequent growing season. Juliatti et al. (1996) andGrothge-Lima (1998) noted that the use of calcium silicate in the soil, as a

Calcium Silicate on Soybean Disease Control 2051corrective and a Si source, increased soybean resistance to stem canker. Lesionlength, caused by the fungus in the pith of diseased plants, was decreased upto 90%. This lesion decrease was linear with the addition of up to 40 mg L −1Si to the nutrient medium (Grothge-Lima, 1998). However, no effect was observedon leaf application of Si. This lack of control could be attributed to Siimmobility in the plant, hindering its movement to the infection court, or to itssole movement in the apoplast. Because soybean is an intermediate type plant,i.e., it absorbs and translocates appreciable amounts of Si when Si is availablein large amounts in the substrate, providing Si through a nutrient solution couldenhance plant resistance to diseases.Disease management has been accomplished through resistant cultivarsand the use of fungicides. Although these methods reduce disease problems,new pathogen races can break resistance within a few years after introduction ofa cultivar. Also, fungicide use is considered a high-technology input, not alwaysavailable for small farmers, in addition to besides being a source of pollutionin the environment when due care is not taken in its handling and spraying.As a consequence, the use of more sustainable strategies for disease controlis highly desirable. Mineral nutrition as a means to increase plant resistanceis sustainable and contributes to soil conservation and to the maintenance ofhuman health. Silicon fertilization may provide an alternative that avoids theseproblems, as research from several countries has shown.This study compared the effect of calcium carbonate and calcium silicatedoses soybean disease control.MATERIALS AND METHODSSoil classified as Ustoxic Quartzipsamment (USA, 1998), was collected in SantaVitória County, located in the state of Minas Gerais, Brazil, in a native forestformation; its chemical characterization is described in Table 1. Its soil wasTable 1Chemical characteristics of the Ustoxic Quartzipsamment soil used in the experimentpH (H 2 O) Ca Mg Al VP K H + Al VCEC B.S. m O.M. Si1:2.5 cmol c dm −3 mg·dm −3 cmol c dm −3 % g kg −1 mg kg −14.6 0.1 0.1 0.7 1.3 19 4.5 4.77 5 74 17 0.6Ca, Mg, Al = (extractor − KCl 1 N); P, K = (extractor − HCl 0.05 N + H 2 SO 40.025 N); H + Al = potential acidity (extractor – calcium acetate); T = CTC pH 7; V= base saturation; MO = (Walkley-Black); Si = (extractor – CaCl 2 0.01 mol L −1 ).CEC = cation exchange capacity; B.S. = base saturation; m = aluminum saturation;O.M. = organic matter.

2052 A. Nolla et al.selected due to its low concentration of available Si (sandy texture) (Beckwithand Reeve, 1963) and, consequently, greater probability of plant response tosoil application of that element.Due to the naturally low fertility of the soil collected, soil fertilization wasperformed by adding, with the aid of a concrete mixer, the equivalent of 400 kgP 2 O 5 ha −1 , 400 kg K 2 Oha −1 , 240 kg magnesium (Mg) ha −1 , and 100 kg of amicronutrient fertilizer in the form of frited trace element (FTE) [9% zinc (Zn),1.8% boron (B), 2% manganese (Mn), 0.8% copper (Cu), 0.1% molybdenum(Mo), and 3% iron (Fe)]. Subsequently, 200 kg lots of the soil were placed in250 L drums 54 cm in diameter × 83 cm in height. The drums were placedin an open and fenced area over crushed rocks to avoid contamination of thesoil in the columns. Excess water in the columns was avoided by punching five1.3 cm diameter holes into the upper and lower ends of the side of the drum.The equivalent of 0, 1500, 3000 (liming requirement), 6000, and12,000 kg ha −1 calcium carbonate (99% CaCO 3 )orcalcium silicate, providedby the company Rockfibras do Brasil (18% CaO and 40% SiO 2 ), was appliedto the column surface (without incorporation), in a randomized block designwith four repetitions, as a 2 × 5factorial experiment (two materials and fivedoses). The soil columns were left fallow for 15 d, then irrigated with 12 L ofwater immediately after the application of the corrective materials to allow fora better reactivity with the soil.The soybean cultivar used was BRS/MG-68 ‘Vencedora,’ which has a determinategrowth habit; average plant height of 80 cm; average insertion height ofthe first pod of 15 cm; purple-colored flowers; brown pubescence; black hilum;good resistance to stalking; good seed quality and resistance to frog’s eye spot(Cercospora sojina), bacterial pustule (Xanthomonas campestris pv glycinea),bacterial blight (Pseudomonas syringae pv glycinea), powdery mildew (Microsphaeradiffusa), and stem canker (Phomopsis phaseoli f.sp. meridionalis).This cultivar is also tolerant to the gall nematodes (Meloydogine incognitaand M. javanica); however, it is susceptible to the cyst nematode (Heteroderaglycines) (EMBRAPA, 2004).Twenty Bradyrhizobium japonicum pre-inoculated seeds were planted onDecember 23, 2003 in the drums, in two rows spaced at 0.25 cm, and werethinned to five plants per row. Soybean seeds were not fungicide treated, so diseasedevelopment could be monitored during the culture cycle. The experimentsimulated direct planting and culture rotation with sugar cane (Saccharum officinarum);therefore, the equivalent of 10 mg ha −1 sugar cane straw mulch wasapplied to the surface of the drums. The soil moisture was maintained throughrainfall or by irrigation (with tap water) during the dry season.Only an insecticide was used for pest (Nezara viridula) control duringthe culture cycle. Evaluation for disease (Peronospora manshurica—Downymildew, Cercospora sojina—frog’s eye spot, and Phakopsora pachyrhizi—Asian rust) was performed at 47, 66, and 79 d after plant seeding. Three plantswere selected per drum, and disease was evaluated using the Horsfall and Barrat

Calcium Silicate on Soybean Disease Control 2053scale (Kranz, 1990), assessing disease incidence by visual evaluation as a percentageof leaves affected per plant by each pathogen.Soybean leaves were collected for nutrient analysis at the flowering stage(R 1 ) (Ritchie et al., 1982) by picking 30 fully expanded leaves without theirpedicels (third leaf from the top meristem of the stem). Leaf Si content wasdetermined using the yellow method (Elliot and Snyder, 1991).Harvest was performed 120 d after seeding; however, Phakopsorapachyrhizi (Asian rust) severity compromised plant development and pod productivityin the experiment, which had to be terminated earlier than planned.Therefore, the soybean canopy was cut and maintained as mulch for a subsequentexperiment.All of the data were submitted to analysis of variance, using the statisticsprogram SANEST (Machado and Zonta, 1991) and the averages compared bythe Tukey test at 5% probability.RESULTS AND DISCUSSIONTissue Si content in soybean demonstrated that, in general, soybean cultivated oncalcium carbonate-treated soil accumulated little Si in the leaves (Figure 1), aswasexpected, because calcium carbonate does not have Si in its composition; thesandy soil had little available Si; and soybean is an intermediate accumulatingplant for Si. According to Marschner (1995), soybean accumulates less than0.23% Si in its tissues. However, under the silicate treatments, greater leafSi content was observed, than under the carbonate treatments. Application ofFigure 1. Leaf Si concentration (%) in soybean cultivar BRS/MG-68 ‘Vencedora,’ as afunction of the application of increasing doses of calcium carbonate or silicate.

2054 A. Nolla et al.calcium silicate increased leaf Si concentration up to 1.70 fold, varying from0.34% to 0.55% if silicate was applied at doses of 0 or 12 mg ha −1 (Figure 1).These values were higher than those reported by Grothge-Lima et al. (1998)(0.02%–0.45%) after the application of 0 or 100 mg Si kg −1 (Si metasilicate—Na 2 SiO 3·5H 2 O) in nutrient solution. These differences could be explained bythe sampling method adopted in each study. Here, the third leaf pair at floweringstage (stage R 1 ), was sampled, whereas Grothge-Lima et al. (1998), sampledstem and leaves at stage V 1 . Therefore, a longer growth period was allowed, andthe plant tissues analyzed could explain the different Si contents between thetwo studies. Also, the increase in Si content under the treatments where silicatewas applied was significant because the soil (Ustoxic Quartzipsamment) studiedhad low natural availability of Si (0.6 mg dm −3 ).The increase in leaf Si concentration in soybean under the treatments wheresilicate was applied is desirable, as supplying silicate has been shown to contributeto reduction of Fusarium solani (soybean sudden-death syndrome) andstem canker in soybean plants (Juliatti et al., 2003). In cucumber, Si acts in thehost tissue, affecting signaling between host and pathogen, which results in afaster and more extensive activation of plant defense mechanisms, probably asa function of phytoalexin production (Samuels et al., 1991; Chérif et al., 1994).The observation of downy mildew incidence on soybean leaves at 47, 66,or 79 d after seeding indicated that the disease was not controlled in the calciumcarbonate plots (Figure 2). However, there was a reduction of downy mildew incidenceunder the silicate treatments, especially at 47 d after seeding (Figure 2a),from 85% (no silicate) to 65% (12 mg ha −1 calcium silicate), demonstrating theefficacy of Si in disease control in the first evaluation. This reduction probablyoccurred as a function of greater Si accumulation in soybean leaf tissue underthe silicate treatments (Figure 1). It is expected that, in cropping areas, thisreduction in disease incidence after soil incorporation of calcium silicate couldalso result in a reduction in use of fungicide sprays, as well as lead to a greateryield due to the longer maintenance of photosynthesizing area.There was no difference in downy mildew incidence 66 d after seeding(Figure 2b); however, where calcium carbonate was applied, there was a trendof greater incidence (90%–100%) than where silicate was applied (81%–92%).This result demonstrates, once again, that the application of calcium silicate wasmore effective for disease control, possibly due to the activation of biochemicalmechanisms of plant defense (Korndörfer et al., 2004). In the last evaluation(Figure 2c), 79 d after seeding, downy mildew incidence was 100% under theliming treatment. Similarly, under the silicate treatments, disease incidence wasnear 100%, varying from 96% to 100%. According to Korndörfer et al. (2004),the incorporation of silicate into the soil does not prevent disease incidence;however, as observed here, it can delay disease onset and reduce its incidenceearly in the growth season. This action is highly desirable, especially consideringthat disease control with fungicides can be delayed, and the number ofsprays reduced, thus reducing production costs.

Calcium Silicate on Soybean Disease Control 2055Figure 2. Leaf incidence (%) of downy mildew (Peronospora manshurica)insoybeancultivar BRS/MG-68 ‘Vencedora’ at (a) 47, (b) 66, and (c) 79 d after seeding, as afunction of the application of increasing doses of calcium carbonate or silicate.Frog’s eye spot was another disease observed during the culture cycle.Although the cultivar BRS/MG-68 ‘Vencedora’ is resistant to this disease(EMBRAPA, 2004), the disease was observed in the experiment, probably dueto favorable environmental conditions. In general, comparing leaf disease incidence,at 47, 66, and 79 d after seeding, it was noted that calcium carbonate didnot control the disease (Figure 3). However, under the silicate treatments, therewas asignificant reduction of frog’s eye spot incidence at 47 d (Figure 3a),from 81% (no silicate) to 14% (12 mg ha −1 calcium silicate), emphasizingthe importance of silicate use for control of frog’s eye spot in the first evaluation.This disease reduction is interesting, for uncontrolled frog’s eye spot canlead to a yield loss of up to 22% (Gupta, 2004). In contrast with its effect ondowny mildew (a reduction of up to 20%, Figure 2a), Si was very effective onfrog’s eye spot control (showing a reduction of up to 67%; Figure 3a). Frog’seye spot incidence (Figure 3) was inversely proportional to leaf Si concentration(Figure 1). Although soybean accumulates little Si in leaf tissues (up to0.55%), the results reported here corroborate that Si reduced frog’s eye spoton the leaves. Possibly, Si accumulation in leaf tissues affected host-pathogen

2056 A. Nolla et al.Figure 3. Leaf incidence (%) of frog’s eye spot (Cercospora sojina)insoybean cultivarBRS/MG-68 ‘Vencedora’ at (a) 47, (b) 66, and (c) 79 d after seeding, as a function ofthe application of increasing doses of calcium carbonate or silicate.signaling, hampering fungal metabolism, and quickly activated plant defensemechanisms, as has been observed in cucumbers (Samuels et al., 1991; Chérifet al., 1994; Marschner, 1995; Korndörfer et al., 2004). Therefore, it is importantto highlight that the presence of Si in leaf tissue can be fundamental toincreasing plant resistance to diseases as a function of toxin synthesis (phytoalexins),which can act as inhibitory or repellent substances for pathogensand pests (Marschner, 1995; Grothge-Lima, 1998; Korndörfer et al., 2003).Calcium carbonate was not effective for the control of frog’s eye spot at 66 dafter seeding (Figure 3b), as expected. Greater resistance to frog’s eye spot wasstill observed under the silicate treatments, which maintained the same controllevel as at 47 d (Figure 3a), varying from 75% (no silicate) to 14% (12 mg ha −1calcium silicate) (Figure 3b). This significant reduction in disease incidencedemonstrated the efficacy of silicate during a good part of the culture cycle (upto 66 d after seeding). These results are in agreement with those of Juliatti et al.(1996), who found greater control of Cercospora blight (Cercospora carotae)and Alternaria blight (Alternaria dauci)incarrot (Daucus carota) treated with

Calcium Silicate on Soybean Disease Control 2057different sources of silicate. Therefore, a reduction in the number of sprays forcontrol of frog’s eye spot can be expected following incorporation of silicate tothe soil. Juliatti et al. (2004a) also observed a reduction of up to 50% in suddendeathsyndrome and stem canker on soybean after silicate incorporation intothe soil. Santos (2002) and Pozza and Pozza (2003) also noted the efficacyof silicate on the control of coffee frog’s eye spot (Cercospora coffeicola).The resistance mechanism of host resistance to the pathogen was probably abiochemical barrier (Bélanger, 2003) or the production of phenol chitinases andperoxidases (Chérif et al., 1994; Fawe, et al., 1998; Epstein, 1999).Frog’s eye spot incidence increased later in the season, as observed fordowny mildew (Figure 3c). There was no disease control under the calciumcarbonate treatments, and the number of diseased plants was greater than 96%;however, under the silicate treatments, disease incidence varied from 100% (nosilicate) to 71% (12 mg ha −1 calcium silicate). This effect probably occurredbecause no disease control measures were employed, and conducting the test inan open area favored fungal proliferation. Moreover, it is important to note that79 d after seeding, soybean was already flowering (R 1 ), and between floweringand grain filling, water and nutrient requirements are at their maximum (Costa,1996); thus, the high nutrient requirement at this stage could reduce soybeannatural resistance to diseases such as downy mildew (Figure 2c) and frog’s eyespot (Figure 3c). According to observations by Korndörfer et al. (2004), soilincorporation of Si sources does not eliminate disease incidence. However, asobserved by Juliatti et al. (2004b), results of disease incidence on soybean couldindicate that field incorporation of silicate has been important in a reductionof the number of fungicide sprays early in the growing season, increasing thegrower’s savings.Nowadays, soybean Asian rust is the most worrisome disease due to its aggressivenessand dissemination speed. In the agricultural year 2003, a minimumof two fungicide sprays were required in 80% of the soybean area, demandingimmediate action and generating extra expense (Yorinori, 2004; Oliveira,2004; Juliatti et al., 2004a). In this study, Asian rust was not observed at 47or 66 d after seeding. However, due to the number of infections and extremelyfast disease progress, at 79 d disease incidence was greater than 96.5% underall treatments, including those with calcium silicate. It is possible that this diseaseprogress occurred because soybean was at the flowering stage (R1) and,according to Julliati et al. (2004a), Asian rust is commonly observed at thisstage. It was expected that leaf Si accumulation (Figure 1) would be effectiveagainst the rust, as it was for downy mildew and frog’s eye spot. In this study,to evaluate the effect of Si on disease control, no chemical control measureswere adopted. Asian rust aggressiveness was so intense that, in 7 d, disease hadpropagated throughout the experiment (Figure 4), leading to premature leafdrop, pod abortion, and complete compromise of yield evaluation and grainproduction. According to Yorinori (2004), the recommendation for Asian rustcontrol is the correct use of adequate doses of proper fungicides.

2058 A. Nolla et al.Figure 4. Leaf incidence (%) of Asian rust (Phakopsora pachyrhizi) onsoybean cultivarBRS/MG-68, ‘Vencedora’ 79 d after seeding, as a function of the application ofincreasing doses of calcium carbonate or silicate.It is possible that the increase in frog’s eye spot (Figure 2) and downymildew (Figure 3) incidence at 79 d after seeding could be due to the occurrenceof Asian rust in the soybeans (Figure 4), thus favoring the development ofdiseases in all treatments. This increase in disease incidence, in turn, couldmean that Si use would be effective for the control of diseases that are not asaggressive, such as frog’s eye spot and downy mildew.CONCLUSIONSA pre-seeding soil application of silicate increased leaf-tissue silicate concentration.This greater leaf concentration was effective on reducing downy mildewincidence at 47 or 66 d after seeding, and frog’s eye spot at all evaluations; however,no control of Asian rust was observed. In contrast, calcium carbonate didnot reduce frog’s eye spot, downy mildew, or Asian rust incidence.ACKNOWLEDGMENTSThe authors acknowledge the Brazilian National Research Council (CNPq) forfinancial support and fellowships.REFERENCESBeckwith, R. S., and R. Reeve. 1963. Studies on soluble silica in soils. 1.The sorption of Si acid by soils and minerals. Australian Journal of SoilResearch 1: 157–168.

Calcium Silicate on Soybean Disease Control 2059Bélanger, R. R., N. Behamou, and J. G. Menzies. 2003. Cytological evidence ofan active role of silicon on wheat resistance to powdery mildew (Blumeriagraminis f.sp. tritici). Phytopathology 23: 402–412.Chérif, M., A. Asselin, and R. R. Bélanger. 1994. Defense responses induced bysoluble silicon in cucumber roots infected by Pythium spp. Phytopathology84: 236–242.Costa, J. A. 1996. Soybean culture (Cultura da soja). Porto Alegre, Brazil:Evangraf.Dixon, R. A. 1986. The phytoalexin response: Elicitation, signaling and controlof host gene expression. Biological Reviews of the Cambridge PhilosophicalSociety 61: 239–291.Elliott, C. L., and G. H. Snyder. 1991. Autoclave-induced digestion for thecolorimetric determination of silicon in rice straw. Journal of Agriculturaland Food Chemistry 39: 118–1119.EMBRAPA. 2004. Technical recommendations for soybean in central Brazil,2003/2004 (in Portuguese) Londrina, Brazil: Embrapa Soja.Epstein, E. 1999. Silicon. Annual Review of Plant Physiology 50: 729–732.Fawe, A., M. Abou-Zaid, J. G. Menzies, and R. R. Bélanger. 1998. Siliconmediatedaccumulation on flavonoid phytoalexins in cucumber. Phytopathology88: 396–401.Fosket, D. E. 1994. Plant growth and development: A molecular approach. SanDiego, CA: Academic Press.Grothge-Lima, M. T. 1998. Inter-relation of stem canker (Diaporthe phaseolorumf. sp. meridionalis), nodulation (Bradyrhizobium japonicum) andsilicon in soybean [Glycine max (L.) Merrill] (in Portuguese), PhDdiss., Centro de Energia Nuclear na Agricultura, Universidade de SãoPaulo.Gupta, G. K. 2004. Major soybean diseases in India: Economic impact andcontrol strategies adopted. Paper presented at the VII World Soybean ResearchConference, IV International Soybean Processing and UtilizationConference, and III Brazilian Soybean Congress, Foz do Iguassu, Brazil,624–630.Hahlbrock, K., and D. Scheel. 1989. Physiology and molecular biology ofphenylpropanoid metabolism. Annual Review of Plant Physiology 40: 347–369.Hartwig, E. E. 1994. Registration of near isogenic soybean germplasm linesD68-0099 and D68-0102, differing in ability to form nodules. Crop Science34: 822.Jones, L.H.P., and K.A. Handreck. 1967. Silica in soils, plants, and animals.Advances in Agronomy 19: 107–149.Juliatti, F. C., E. N. Borges, R. R. L. Passos, J. C. Caldeira Jr., F. C. Juliatti, and A.M. Brandão. 2003. Soybean diseases (in Portuguese) Cultivar—GrandesCulturas 47 (supplement): 3–14.

2060 A. Nolla et al.Juliatti, F. C., M. G. Pedrosa, R. M. Q. Lanna, C. H. Brito, and B. Mello 2004b.Influence of silicon on the reduction of seedling damping off (Fusariumsemitectum)insoybean (in Portuguese). Bioscience Journal 20: 57–63.Juliatti, F. C., A. C. Polizel, and F.C. Juliatti. 2004a. Integrated disease managementin soybeans (in Portuguese) Uberlândia, Brazil: Composer Gráfica eEditora.Juliatti, F. C., F. A. Rodrigues, G. H. Korndörfer, O. A. Silva, and J. R. Peixoto.1996. Effect of silicon in resistance induction against Diaporthe phaseolorumf.sp. meridionalis in soybean cultivars with different resistance levels(Efeito do silício na indução de resistência a Diaporthe phaseolorum f.sp.meridionalis em cultivares de soja com diferentes níveis de resistência).Fitopatologia Brasileira 21(supplement): 26.Korndörfer, G. H., H. S. Pereira, and M. S. Camargo. 2004. Calcium and magnesiumsilicates in agriculture (in Portuguese), 3rd edition. Uberlândia,Brazil: GPSi/ICIAG/UFU.Kranz, J. 1990. Monitoring epidemics: disease. In Introduction to plant disease,eds. C.L. Campbell and L. V. Madden, 107–128. New York: John Wiley.Machado, A. A., and E. P. Zonta. 1991. User’s Guide for Sanest: A system forstatiscal analyses in microcomputers (in Portuguese) Rio Grande do Sul,Brazil: UFPel.Marschner, H. 1995. Mineral nutrition of higher plants. 2nd edition; New York:Academic Press.Menzies, J. G., and R. R. Bélanger. 1996. Recent advances in cultural managementof diseases of greenhouse crops. Canadian Journal of Plant Pathology18: 186–193.Menzies, J. G., D. L. Ehret, A. D. M. Glass, and A. L. Samuels. 1991. The influenceof silicon on cytological interactions between Sphaerotheca fuligineaand Cucumis sativus. Physiological and Molecular Plant Pathology 39:403–414.Miyake, Y., and E. Takahashi. 1995. Effect of silicon on the growth of soybeanplants in a solution culture. Soil Science and Plant Nutrition 31: 625–636.Morgan-Jones, G. 1989. The Diaporthe/Phomopsis complex: Taxonomic considerations.Paper presented at the IV World Soybean Research Conference,Buenos Aires, Argentina, 1699–1706.Oliveira, A. C. B. 2004. Soybean rust: Season 2002/2003 in Bahia. Paper presentedat the VII World Soybean Research Conference, IV InternationalSoybean Processing and Utilization Conference, and III Brazilian SoybeanCongress, Foz do Iguassu, Brazil, 1308–1312.Peters, N. K., and D. P. S. Verma. 1990. Phenolic compounds as regulatorsof gene expression in plant-microbe interaction. Molecular Plant MicrobeInteractions 3: 4–8.Pozza, E. A., and A. A. A. Pozza. 2003. Plant disease management with macroandmicronutrients (in Portuguese). Fitopatologia Brasileira 28: S52–S54.

Calcium Silicate on Soybean Disease Control 2061Ritchie, S., J. J. Hanway, and H. E. Thompson. 1982. How a soybean plantdevelops, (Special Report, 53). Ames, IA: Iowa State University of Scienceand Technology.Samuels, L., A. D. M. Glass, D. L. Ebret, and J. G. Menzies. 1991. Mobilityand deposition of silicon in cucumber-plants. Plant Cell and Environment14: 485–492.Santos, D. M. 2002. Effect of silicon on frog’s eye spot (Cercospora coffeicolaBerk & Cooke) on coffee (Coffea arabica L.) seedlings (in Portuguese),master’s thesis, Universidade Federal de Lavras.United States Department of Agriculture, Natural Resources Conservation Service,Soil Survey Staff. (USA) 1998. Keys to soil taxonomy. 8th editionWashington, DC: Department of Agriculture.Yorinori, J. T. 2004. Soybean rust: An overview (in Portuguese) Paper presentedat the VII World Soybean Research Conference, IV InternationalSoybean Processing and Utilization Conference, and III Brazilian SoybeanCongress, Foz do Iguassu, Brazil, 1299–1307.